New insights into the distribution patterns of Mediterranean insular endemic plants: The Sicilian islands’ group

This study aimed to shed further light on the factors that play a significant role in the spatial distribution of Mediterranean endemic plants. A multiple linear regression was applied to identify which environmental variables influence significantly the range size of the strictly endemic plants from Sicily and its satellite islands, including the Maltese archipelago. The statistical analysis included 202 taxa and 27 environmental variables of which 19 were bioclimatic predictors and 8 were related to habitat, altitude, bedrock and land use. The regression analysis showed that the amount of explained variation in the range size was 57.6%. The environmental variables affecting endemic range size decreased in this order of significance: number of colonized habitats > species altitudinal range > mean temperature of the wettest three months > minimum temperature of the coldest month > bedrock-preference indifference > annual mean temperature. In particular, basophilous and acidophilous endemics showed similar range sizes; bioclimatic variables highlighted the phytogeographical role of geomorphology; land use, instead, did not prove a significant predictor of species range size. Another finding showed that there are no habitats more prone than others to favor a larger endemic range size. Results suggested also that the narrow distribution of mountain endemics should be mainly attributed to niche specialism rather than spatial constraints. Overall, a complex picture emerged from the analysis of the distribution patterns of the Sicilian endemic plants. On the one hand, this study showed how important species ecological adaptability and local geomorphology are to predict range size. On the other hand, endemic plant distribution should be also explained through the complex climatic and geological history of Sicily and its satellite islands.